Magma
Magma is the melted rock under the ground.[1] The liquid rock may have solid bits mixed in with it, and volcanic gas.
There are different types of magma. One is called felsic magma. Felsic magma is thick and has silica minerals. It mostly makes light-coloured rocks. Another type is called mafic magma, which is runny and has less silica. It usually makes dark-coloured rocks. Magmas can be intermediate between both types.
Magma may become solid by cooling slowly below the surface. This makes "plutonic" rocks such as granite. When magma comes out from the ground in a volcano it is called lava. Lava cools quickly, and forms other kinds of rock such as basalt.
Magma is produced by melting of the Earth's mantle or the crust. It happens at tectonic settings, such as subduction zones, continental rift zones,[2] mid-ocean ridges and hotspots.
Melted material from the mantle and crust moves up through the crust and collects in magma chambers.[3][4]
When they come up through the crust, magmas may feed a volcano and come out as lava. But they may solidify underground to form an intrusion (magma which cools and becomes solid).[5] Intrusions eventually cool down and become igneous dikes or sills.
The study of magma is usually done in lava flows. However, magma was found under the ground three times in geothermal drilling projects—twice in Iceland and once in Hawaii.[6][7][8][9]
Magma Media
Phase diagram for the diopside-anorthite system
Schematic diagrams showing the principles behind fractional crystallisation in a magma. While cooling, the magma evolves in composition because different minerals crystallize from the melt.
A single silica tetrahedron
Two silica tetrahedra joined by a bridging oxygen ion (tinted pink)
References
- ↑ Bowen, Norman L. (1947). "Magmas". Geological Society of America Bulletin. 58 (4): 263. doi:10.1130/0016-7606(1947)58[263:M]2.0.CO;2. ISSN 0016-7606.
- ↑ Foulger, G.R. (2010). Plates vs. Plumes: A Geological Controversy. Wiley–Blackwell. ISBN 978-1-4051-6148-0.
- ↑ Detrick, R. S.; Buhl, P.; Vera, E.; Mutter, J.; Orcutt, J.; Madsen, J.; Brocher, T. (1987). "Multi-channel seismic imaging of a crustal magma chamber along the East Pacific Rise". Nature. 326 (6108): 35–41. Bibcode:1987Natur.326...35D. doi:10.1038/326035a0. ISSN 0028-0836. S2CID 4311642.
- ↑ Sparks, R. Stephen J.; Cashman, Katharine V. (2017). "Dynamic Magma Systems: Implications for Forecasting Volcanic Activity". Elements. 13 (1): 35–40. doi:10.2113/gselements.13.1.35. ISSN 1811-5209.
- ↑ McBirney, A.R.; Noyes, R.M. (1979-08-01). "Crystallization and Layering of the Skaergaard Intrusion". Journal of Petrology. 20 (3): 487–554. Bibcode:1979JPet...20..487M. doi:10.1093/petrology/20.3.487. ISSN 0022-3530.
- ↑ Scientists' Drill Hits Magma: Only Third Time on Record, UC Davis News and Information, June 26, 2009.
- ↑ Magma Discovered in Situ for First Time. Physorg (December 16, 2008)
- ↑ Puna Dacite Magma at Kilauea: Unexpected Drilling Into an Active Magma Posters Archived 2011-06-06 at the Wayback Machine, 2008 Eos Trans. AGU, 89(53), Fall Meeting.
- ↑ Teplow, William; Marsh, Bruce; Hulen, Jeff; Spielman, Paul; Kaleikini, Mike; Fitch, David; Rickard, William (2009). "Dacite Melt at the Puna Geothermal Venture Wellfield, Big Island of Hawaii" (PDF). GRC Transactions. 33: 989–994. Retrieved 8 February 2021.